3 months and waiting for my line to be made available to my ISP.

I have waited three months for them to remove the previous ISP from my fibre line. I have sent through proof of address and been talking to them through my current ISP. I have even done the legwork for them to find out that the line in my flat is definitely not being used by another ISP. Why it takes so long to get their admin in order is beyond me. avoid at all costs